Abstract
Background
Recent publications have supported the anatomic placement of anterior cruciate grafts to optimise knee function. However, anatomic placement using the anteromedial portal has been shown to have a higher failure rate than traditional graft placement using the transtibial method. This is possibly due to it being more technically difficult and to the short femoral tunnel compromising fixation methods. It also requires the knee to be in hyper flexion. This position is not feasible during with a tourniquet in situ on the heavily muscled thighs of some athletes.
Hypothesis: That navigation can be used to place the femoral tunnel in the anatomic position via a more medial transtibial tunnel.
Methods
25 patients underwent Navigated Anterior Cruciate reconstruction with quadruple hamstring grafts. The Orthopilot™ 3.0 ACL (BBraun Aesculap, Tuttlingen) software was used. The femoral and tibial ACL footprints were marked on the bones with a radio frequency probe and registered. The pivot shift test, anterior drawer and internal and external rotation were registered. A navigated tibial guide wire was inserted at 25° to the sagittal plane and 45° to the transverse plane exiting through the centre of the tibial footprint. The guide wire was advanced into the joint to just clear of the surface of the femoral footprint with the knee in 90° flexion. Flexion/extension of the knee was done to determine the closest position of the guide wire tip to the centre of the anatomical femoral footprint. If the tip was within 2mm of the centre of footprint, the position was accepted. If not the tibial guide wire was repositioned and the process repeated. The tibial tunnel was drilled, followed by transtibial drilling of the femoral tunnel. A screen shot was done to allow determination of the shape and area of the tunnel aperture relative to the femoral footprint using ImageJ (National Institute of Health). The graft was fixed proximally with an Arthrex ACL Tightrope® and distally with a Genesys™ interference screw. The pivot shift test, anterior drawer and internal and external rotation were repeated and recorded using the software.
Results
In 22 out of 25 patients the centre of the drill hole was within 2mm of the centre of the anatomic femoral footprint. In 3 patients it was between 2 and 4 mm off centre. The femoral tunnel diameter ranged from 7.5mm to 9.5mm. In 23 knees there was more than 80 % overlap between the tunnel aperture and the anatomical footprint. In the other 2 knees there was 65% and 75% overlap respectively. The direction of the final tibial tunnel ranged from 22° to 28° from the sagittal plane and 42° to 49° from the transverse plane. The optimum knee flexion was between 76° and 94°. In all cases, the pivot shift recorded by the software was absent after graft fixation. There was a statistically significant difference between the anterior drawer, internal and external rotation before and after graft fixation (p<0.05)
Conclusion
Based on our data, navigation allows reproducible transtibial anatomic placement of the quadruple hamstring ACL graft. This is possible when the position of the tibial tunnel is customised to the anatomy of the individual patient's knee.
